Process of making same



Sept. 27, 1938. E. s, MERRIAM Re. 20,868

PREFORMED ABRASI-VE ARTICLE AND PROCESS OF MAKING SAME Original Filed Sept. 17, 1935 awe/whom UNITED STATES PATENT OFFICE PREFORMED ARTICLE AND PROCESS OF MAKING SAME Edmund S. Merriam, Marietta, Ohio Original No. aosmna'uatea August 4, 1936, Serial No. 41,003, September 17, 1935. Appliggiigno for reissue July 28, 1938, Serial No.

14 Claims. (Cl. 51-278) This invention relates to preformed abrasive heat necessary to produce the vitrified bond in articles and a process for making the same. the wheel is generated in the wheel itself with- More particularly the invention contemplates the out the application of extraneous heat such as provision of a novel, efiicient, and economic procrequired in kiln firing.

5 es for producing abrasive wheels of superior While the inventioninits broader aspect com 6 quality. prehends any of many modes of generating the According to current practice, abrasive grindnecessary heat to form the vitrified bond in situ ing wheels are composed of grains or grit of hard in the wheel, rm] preferred method will be first abrasive material, generally oxide of aluminum described. In this method the abrasive grains 10 or silicon carbide bonded together by a suitable or grits are mixed with the necessary known 10 bonding agent. The nature of the bonding maingredients to form the required bond in the terial and its quantity determine, to a large exfinished wheel. With this mixture'there is incortent, the character of the wheel and the uses to porated in uniformly distributed form a comwhich it may be put. bustible material ofsuch character and in such Both organic and inorganic bonding materials amount as to generate sufficient heat, upon bum- 15 are used, the latter, however, being the most ing, to produce the bond in situ. common. The usual bonding material comprises The combustible material employed must be a vitrified substance resembling porcelain prosuch as will not react so vigorously as to cause duced by a controlled process of heating in some violent escape of volatile products, and it must form of kiln. not leave any objectionable non-volatile residue 20 In the manufacture of vitrified abrasive artiin the wheel. I have found petroleum coke or eles, the abrasive grains or grits are mixed with coke produced from coal tar to function very clays of the desired qualities together with feldsatisfactorily in the process since it produces spar, flint, or like materials and water. The substantially no ash. Other-combustible matemixture is then formed into the desired shape, rials possessing the above defined characteristics 25 such as a wheel, by molding or the like. The are, or course, suitable for use. wheel is then dried and placed in a kiln. The Because clays, feldspar, and flint form a hetcharacteristics of the wheel are controlled to some erogeneous system in which reaction may be slow, extent by varying the amount and nature of the I prefer to use materials for forming the bond in bond employed as well as by the subsequent heat a prefused or fritted condition sothat only a rela- 30 treatment. tively simple fusion is required to-be effected in Both continuous tunnel type and intermittent the wheel. I can if desired, of course, add more pottery type kilns are currently employed for readily fusible materials, such as borax, cryolite, the heat treatment of the wheels. In the tunnel and the like, to act as a flux.

typ k s u y around four s are required In order to reach temperatures in the wheel 35 to mature and co l the wheels. In he po tery of from 1000" to 150o c., it is necessary to use type kilns, it may require as long as three weeks only from 4% to 8% by weight of carbon or its to produce the finished wheel. The use of any equivalent. in the wheel when the burning is etkiln is expensive and requires a large investjected in an atmosphere of oxygen. Slightly 40 ment. The consumption of large amounts o more is required when the burning is effected 40 fuel and the time factor in kiln firing are imsolely through t s of i portant items in the production costs because It will, of course, be understood that in preof the necessity of retaining for long periods the forming the wheel before heat treatment, any of arches, s l and entire kiln at the reqthe conventional temporary bonding agents may uisite temperature. be employed such as dextrine and Bakelite which 5 It is the purpose of the present invention to burn off completeljpin the heat treating step. completely obviate the necessity for kiln firing The character of-the final wheel can be accuin the production of vitrified abrasive wheels. rately controlled, as well as its porosity, by vary- By the present invention, the great fuel costs ing the nature and physical structure of the inincident to the manufacture of vitrified abrasive corporated combustible material. For example, 50 wheels are reduced to a minimum as are the if finely powdered coke is used, the finished wheel labor costs and capital investment. Furtherwill be more dense than when granular coke is more, the production of my improved abrasive used. This is due to the fact that the burning wheel is reduced to a. one-day operation. out of the combustible material leaves voids in In accordance with the present invention, the the wheel comparable in size and number with 55 the individual elements of the combustible material employed. If a wheel of a high degree of porosity is desired, a less dense form of combustible material is used, such for example as charcoal, which is much more bulky than coke, for a given heat development in the wheel. It is possible to use such carbonaceous materials as corn meal, cork particles, and the like. Due to the water produced in their combustion, however, it is preferable to bond the wheel weakly with water glass and then pre-char the woody materials at a low heat. This expedient need be resorted to only in the event that highly porous wheels are desired. 1

In preparing the mixture which is to form the the retort.

A suitable retort for carrying out the process of the present invention is illustrated in thesecompanying drawing.

The retort embraces the outer cylinder l of thin metal and the somewhat heavier top 2 and bottom 3. The cylinder l carries annular flanges 4 and 5 at the top and bottom, respectively, adapted to cooperate with the peripheral flanges 6 and] at the top 2 and bottom 3. A suitable deformable metal washer 8 is clamped between the flanges 4 and G at the top, and a similar washer 9 is clamped between the flanges 5 and I at the bottom. The bottom 3 may, of course, be permanently united to the cylinder I. As illustrated, however, both the top 2 and bottom 3 are removable by simply taking out the clamping bolts l0.

The top 2 and bottom 8 are reinforced by angle iron struts ll welded thereto. The top is pro,- vided with a central opening l2 and the bottom with an opening l3. An inlet pipe I4 has a gastight fit with the opening l2 and is provided with valve controlled branch lines l5 and 16 for air and oxygen. There is also mounted on the line l4 a suitable pressure gauge I! for observing the pressure conditions prevailing in the retort. Immediately below the opening I 2 in cover 2, there is suspended by rods I8 a baflle member l9 to prevent channeling of the incoming air or oxygen. An outlet pipe 20 for combustion gases and cooling air has a gas-tight fit in the opening [3 in the bottom of the retort. The retort carries trunnions 2| that permit it to -be inverted for removal of its charge of treated wheels.

A free circular space having a diameter somewhat greater than that of the wheels to be treated is provided at the bottom immediately above the outlet line 20. This space is between the bottom 3 and the perforated plate or screen 22 suitably supported'a few inches above the bottom. An open-ended cylinder 23 having a diameter somewhat greater than that of the wheels to be treated is disposed in concentric relation to the outer cylinder 1. The annular space between the cylinders l and 23 is packed with suitable insulating material; A sparkplug 24 is fitted into the cover 2,,and a coil of readily ignitible thin iron wire 25 is attached to its terminals.

the bottom of the cylinder 23 and supported on A baflle plate 21 may.

the perforated plate 22. advantageously be set in the bed. The first green wheel containing the requisite amount of combustible material is next laid on the bed and has free granular material filled in around its circumference and in its axial opening. There is then placed over the first wheel a layer of like granular material having mixed therewith coke or other combustible material but no binding agents of any kind. This layer transmits combustion directly from the wheel above to the wheel below, but since it contains no bonding material, the grains remain free after the burning operation, and the layer acts to keep the wheels sepa- -rated as individual units. The next wheel is then laid in and the operation repeated until the retort'is filled. As illustrated, the retort has :3. capacity of twelve wheels. The top wheel is covered with alayer of grains and admixed coke, and there is also advantageously provided a layer of a suitable readily ignitible substance in immediate proximity to said iron wire coil 25.

When the retort is packed, the cover 2 is affixed in sealed relation thereto and oxygen supplied through the line I5. Suitable means such as a flow meter (not shown) may be provided in the lines l4 and 20 for accurately controlling the rate of flow of air or oxygen through the retort. A switch (not shown) in the spark plug circuit is next closed, which effects ignition in the retort. After ignition has been eiiected, excess air may be supplied through line IS in substitution for all or a part of the oxygen being supplied through line l5.

It will be apparent from the arrangement of the wheels and the surrounding packing material that I provide a highly symmetrical retort charge and that the air or oxygen is caused to flow as a confined draft symmetrically through the wheels,- insuring uniform burning thereof.

The burning takes place very rapidly and can be controlled by the pressure at which the air or oxygen is supplied and the rate of flow thereof through the retort. Ordinarily burning is complete in from twenty tothirty minutes when substantially pure oxygen is employed. When air is air through the retort, the cooling time can be reduced to around eight hours without deleterious effects. i

The current difliculty of non-uniformity of wheels from one run to the next is completely overcome in my process. I need employ no temperature measuring instruments of any kind since, by precise measurement of the fuel introduced to the wheel mix and control of the flow of the gas, a consistently uniform product necessarily results.

It is possible in the molding of the wheels to form on one side thereof a thin layer of grains and admixed coke with a temporary binder only therein. The premolded wheels carrying such layers may then be rapidly placed in the retort free unbonded grain layers separating the vitrified abrasive wheels.

In some instances it may be advantageous to include coke in the free grains that are packed around the periphery of thegreen molded wheels in the retort.- This expedient furnishes additional heat and insures complete reaction at the rims of the wheels.

In the production of thin dense wheels, it is sometimes desirable to generate all the heat in the intermediate layers and surrounding grains without the necessity of incorporating the combustible material in the wheel mix.

Having thus described my invention, claim is:

1. In a process for manuiacturing abrasive articles, the steps of forming a plurality of green abrasive articles containing abrasive grains, reagents adapted upon subjection to adequate heat to form a vitreous bond between said grains, and a combustible material, placing said green articles in a retort and separating the same therein by interposed segregating layers containing a combustion supporting substance, and'igniting and burning in said retort said combustible material in said articles and combustion maintaining substance in said segregating layers to thereby generate the requisite heat within the retort to form a vitreous bond between the abrasive grains in what I said abrasive articles.

2. A process for producing abrasive articles comprising mixing suitable abrasive grains with a vitrifiable bond and a combustible material sufficient in amount, when burned in situ, to generate adequate heat within the article to efiect binding of said abrasive grains by said vitrifiable bond, forming the mixture into the desired shape, and igniting and burning said combustible material.

3. A process for producing abrasive articles comprising mixing suitable abrasive grains with a vitriflable bond, including in the mixture combustible material sufficient in amount, when burned in situ, to generate adequate heat in said article to form a vitreous bond between said abrasive grains, and thereafter igniting and burning said combustible material.

.4. A process for producing abrasive articles comprising mixing suitable abrasive grains with a previously fused vitreous binding material in finely divided form, including in the mixture a temporary binder and a substantially non-residue producing combustible material suflicient in amount, when burned in situ, to generate adequate heat in the article to re-fuse said vitreous binding material, forming the mixture into the desired shape, and then igniting and burning said combustible material.

5. A process for producing abrasive articles comprising mixing suitable abrasive grains with vitrifiable reagents adapted upon being subjected to adequate heat to produce a vitreous bond between the abrasive grains, including in the mixture a combustible material suflicient in amount, when burned in situ, to generate adequate heat to cause said vitrifiable reagents to form a vitreous bond, forming the mixture in the desired shape, and then burning said included combustible material.

6. A process for producing abrasive articles comprising mixing suitable abrasive grains with reagents capable, upon being subjected to adequate heat, of reaction and fusion to produce a vitreous bond, including in the mixture a temporary binder and a substantially non-residue producing combustible material sufilcient inamount, when burned in situ, to generate adequate heat to effect reaction and fusion of said reagents to form a vitreous bond, forming the mixture into the desired shape, and'then said combustible material. 1

'I. A process for producing abrasive wheels and the like comprising mixing suitable abrasive grains, a previously fused vitreous bonding material in finely divided form, a temporary binder, and a substantially non-residue producing combustible material sufficient in amount, when burned in situ, to generate adequate heat to again fuse said vitreous bonding material, molding a plurality of green wheels, placing said wheels in a retort with intervening layers of bond-free abrasive grains, and igniting and burning said combustible material. 7

8. A method for producing abrasive wheels comprising mixing suitable abrasive grains with a vitrifiabl'e bond and combustible material adequate in amount, when burned in situ, to generate sufiicient heat to produce from the vitrifiable burning bond a vitreous bond between said abrasive grains,

forming a plurality of temporarily bonded wheels, placing said temporarily bonded wheels in a retort wherein each individual wheel is surrounded by unbonded abrasive grains similar in character to those included in the wheels, and igniting and burning the combustible material in situ in the wheels in said retort to produce a, vitreous bond between the abrasive grains in each wheel.

9. In a process for manufacturing abrasive articles, the steps of forming a plurality of green abrasive articles containing abrasive grains, bonding material adapted upon subjection to adequate heat to form a vitreous bond between the grains, and a combustible material, placing said green articles in a retort, segregating the same therein burned in situ, to generate 'suificient heat to produce from the vitrifiable bond producing material a vitreous bond between said abrasive grains,

forming a plurality of wheels from such mixture, packing said temporarily bonded wheels in a retort by surrounding each wheel with segregating material, and igniting and burning the combustible material in situ in the wheels in said retort'by passing a confined draft of a combustion-supporting gas symmetrically through said wheels to thereby uniformly burn said wheels and produce a vitreous bond between the abrasive grains in each wheel.

11. A process for producing abrasive wheels comprising mixing suitable abrasive grains, a bonding material, a temporary binder, and a combustible material sufiicient in amount, when burned in situ, to generate adequate heat to fuse said bonding material, molding a plurality of green wheels, packing said wheels in a retort with intervening layers of segregating material, and igniting and burning said combustible material by effecting a positive flow of a combustion-suppo ting gas symmetrically through said wheels to uniformly bond the abrasive grains in each wheel.

12. A process for producing preformed abrasive articles comprising initially molding the articles in the desired form from a mixture comprising suitable abrasive grains, bonding material adapted upon being subjected to adequate heat to produce a vitreous bond between the abrasive grains, and a temporary binder, packing the preformed articles in a retort by surrounding each individual article with segregating material so as to provide a symmetrical retort charge, including in said retort, charge, in association with each preformed abrasive article therein, combustible material sufllcient in amount, when burned in situ, to generate adequate heat to form, from said bonding material, a vitreous bond between the abrasive grains in each article, and burning said combustible material in said retort by eifecting a positive flow of combustion-supporting gas through the articles and segregating material in said retort charge.

13. A process for producing'preformed abrasive articles comprising initially molding the articles in the desired form from a mixture comprising suitable abrasive grains, bonding material adapted upon being subjected to adequate heat to produce a vitreous bond between the abrasive grains, and

a temporary binder, packing the preformed artiao,sea

cles in a retort by surrounding each individual article with segregating material so as to provide a symmetrical retort charge, including in said segregating material combustible material sufilcient in amount, when burned in situ, to generate adequate heat to form, from said bonding material, a vitreous bond between the abrasive grains in each article, and burning said combustible material in said retort by effecting a positive flow of combustion-supporting gas through the articles and segregating material in said retort charge. I

14. Aprocess for producing preformed abrasive articles comprising initially molding the articles in the desired form from a mixture comprising suitable abrasive grains, bonding material adapted upon being subjected to adequate heat to produce a vitreous bond between the abrasive grains, and a temporary binder, superposing a plurality of such preformed articles symmetrically inan insulated enclosure, each of said superposed articles being surrounded by granular material, and each of said superposed articles having combustible material associated therewith in suflicient amount, when burned in'situ, to generate adequate heat to form a vitreous bond between the abrasive grains in each article, and burning said combustible material by passing combustionsupporting gas through said superposed articles.

'- EDMUND S. MERRIAM. 

